Fluid pump

ABSTRACT

The present invention inhibits suction of dust and moisture into a drive chamber for driving a piston of a fluid pump while reducing drive load through feeding/discharging of fluid to/from the drive chamber. In the interior of a cylinder, a pressure increasing/decreasing chamber is formed between a valve unit on the cylinder head side and the piston. On the opposite side of the pressure increasing/decreasing chamber, the drive chamber is disposed. There are provided a ventilation path for communicating the drive chamber and the outside space, a fluid path connected to the feeding/discharging space of the valve unit, a merging space where the fluid path is merged with the ventilation path midway, and a fluid filter provided in the merging space.

TECHNICAL FIELD

The present invention relates to a fluid pump configured to effectfeeding/discharging of a fluid through movements of a piston. Moreparticularly, the invention relates to a technique for controllingfeeding/discharging of a fluid to/from a drive chamber in which thereare disposed a connection rod connected to the piston, a crankmechanism, etc.

BACKGROUND ART

As an example of a fluid pump, PTL 1 discloses a vacuum pump including apiston mounted inside a cylinder to move back and forth therein, adriving means configured to convert a drive force of a motor into areciprocal movement via a crank mechanism and transmit this reciprocalmovement to the piston, and a valve body having an intake valve and adischarge valve and mounted in the cylinder head.

In this PTL 1, at a position near a drive chamber (a crank chamber inthis document) accommodating a crank mechanism, there is disposed acase; and in the cylinder wall, there is formed a discharge gas path forfeeding discharge gas of a valve body to the interior space (a devicechamber) of the case. The drive chamber and the interior space (thedevice chamber) of the case are communicated via a drive chamber sidedischarge port. And, the case forms a relief chamber side discharge portfor discharging discharge gas present in the interior space into theatmosphere. With this, at the time of operation of the piston, thedischarge gas is caused to flow through the discharge gas path, thecrank chamber, the drive chamber side discharge port, the device chamberand the relief chamber side discharge port in this mentioned order, thusbeing discharged to the outside and variation in the pulsating pressureat the time of discharging is restricted, thus restricting gasdischarging noise.

Further, as an example of a fluid pump, PTL 2 discloses a compressor (anair compressing mechanism) configured as follows. A piston is mountedinside a cylinder to be movable back and forth. A valve assembly isprovided in a cylinder head at an upper portion of a cylinder. A crankcase is disposed at a lower portion of the cylinder and a cross-slidercrank mechanism as a crank mechanism mounted inside this crank case andthe piston are operably coupled with each other via a piston rod.

According to an arrangement of this PTL 2, an air passage is formed in asupport member provided at a lower portion of the cylinder. And, to thisair passage, a sealed chamber is connected (the arrangement shown inFIG. 5 in the document). According to an alternative arrangement of thedocument, to the air passage above, an air filter is connected (thearrangement shown in FIG. 6, FIG. 9, etc. in the document). With thesearrangements, when there occurs a drop in the pressure in the spacedownwardly of the piston (the side opposite the cylinder head) inassociation with a movement of the piston, air of the chamber is suckedor the ambient air is sucked via the air filter (an air cleaner in thedocument). Conversely, when there occurs a rise in the pressure in thespace downwardly of the piston, the air of this space is sent out to thesealed chamber or the air is discharged to the outside via the airfilter. With these arrangements, reduction of the operational load issought for and rise of temperature inside the cylinder is restricted.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.    2011-7118-   PTL 2: Japanese Unexamined Patent Application Publication No.    10-266966

SUMMARY OF INVENTION

With a fluid pump configured to feed/discharge fluid to/from a space onthe side of the piston head in association with piston movements, at thetime of reciprocal movements of the piston, pressure variation occursalso in the drive chamber (the space in which the crank mechanism etc.are mounted) opposite the piston head. And, in case this drive space isconfigured as a sealed space, the pressure variation in the drivechamber acts as a “drive load” on the actuator.

In order to resolve the above inconvenience, it is conceivable toarrange such that feeding/discharging of fluid to/from the drive chamberis made possible from the outside, as described in PTL 1 or PTL 2. Inparticular, with the configuration of the vacuum pump disclosed in PTL1, at the time of movement of the piston in the discharging direction,there occurs no waste in the flow of the fluid as the discharge air fromthe space on the side of the cylinder head is guided to the drivechamber. With the configuration of the compressor (air compressingmechanism) disclosed in PTL 2 (the configuration shown in FIG. 6, FIG. 9of the document), there occurs no waste in the flow of the fluid as aportion of the fluid of the drive chamber is fed to the cylinder at thetime of movement of the piston in the feeding direction. With use ofthese arrangements, the load on the motor driving the piston isalleviated.

However, in a fluid pump configured to feed/discharge fluid inassociation with piston movements, when fluid is sucked to the drivechamber which has reached a negative pressure state, if dust and/ormoisture is/are contained in this fluid, this will invite operationfailure of the drive system, and/or corrosion thereof. In this regard,there is room for improvement.

The object of the present invention is to configure a fluid pumprationally which is capable of restricting suction of dust and/ormoisture into the drive chamber while reducing the dive load throughfeeding/discharging of fluid to/from the drive chamber that drives apiston.

According to a characterizing feature of the present invention, a fluidpump comprises:

a cylinder;

a piston mounted inside the cylinder to be moved back and forth, thepiston partitioning the inside of the cylinder between a pressureincreasing/decreasing chamber on the side of the cylinder head and adrive chamber opposite the pressure increasing/decreasing chamber;

a valve unit having a control space for causing fluid of the pressureincreasing/decreasing chamber to act on a pressurizing/depressurizingobject and a feeding/discharging space for feeding/discharging fluidbetween the pressure increasing/decreasing chamber and the outsidespace, the valve unit being provided in the cylinder head so as tocontrol flow of the fluid to the pressure increasing/decreasing chamberat the time of a reciprocal movement of the piston:

a ventilation path communicating the drive chamber and the outside spacewith each other;

a fluid path connected to the feeding/discharging space of the valveunit;

a merging space in which the fluid path is merged with the ventilationpath midway; and

a fluid filter mounted in the merging space.

With the above-described arrangement, when the drive chamber reaches anegative pressure state as the piston is moved in the dischargingdirection, the fluid from the ventilation path is sucked to the drivechamber with the fluid being filtered through the fluid filter.Simultaneously, the fluid from the fluid path connected to the mergingpath is also sucked to the drive chamber. Conversely, when the drivechamber reaches a positive pressure state as the piston is moved in thesucking direction, the fluid from the drive chamber is sent from theventilation path to the outside while being filtered through the fluidfilter. Simultaneously, a portion of the fluid of the drive chamber isfed to the fluid path connected to the merging path.

As a result, there is realized a fluid pump capable of restrictingsuction of dust and/or moisture into the drive chamber while reducingthe dive load through feeding/discharging of fluid to/from the drivechamber that drives a piston. In particular, with the above-describedarrangement, at the time of movement of the piston, there would normallyoccur a feeding/discharging noise in association with variation in thepressure of the drive chamber. But, since the ventilation path and thefluid path are connected to this drive chamber, sharp variation in theair pressure of these spaces is restricted, so that noise restrictioneffect is achieved.

In the present invention, preferably, the valve unit includes:

an intake valve disposed in the control space and configured to beopened only when the piston is operated in the sucking direction forsucking air as the fluid from a depressurizing object as thepressurizing/depressurizing object to the pressure increasing/decreasingchamber;

a discharge valve disposed in the feeding/discharging space andconfigured to be opened only when the piston is operated in thedischarging direction for feeding air as the fluid to the pressureincreasing/decreasing space; and

a discharging path as the fluid path for feeding air from the dischargevalve to the merging space.

With the above-described arrangement, when the piston is operated in thesucking direction, air from the depressurizing object is sucked via theintake valve into the pressure increasing/decreasing chamber and also inassociation with rise in the pressure of the drive chamber, the air ofthe drive chamber is sent from the ventilation path to the outsidespace. Conversely, when the piston is operated in the dischargingdirection, the discharge valve is opened to feed the air of the pressureincreasing/decreasing chamber to the discharge path as the fluid path.At the time of this operation, a negative pressure is developed in thedrive chamber. So, the air of the outside space is sucked via theventilation path into the drive chamber as being filtered through thefluid filter and also the air from the fluid path merged with thisventilation path is sucked into the drive chamber. That is, the airsucked from the outside space into the drive chamber is always filteredthrough the fluid filter, whereby dust and/or moisture will be removedtherefrom. And, a portion of the air fed to the discharge path from thepressure increasing/decreasing chamber at the time of this suckingoperation is sucked into the drive chamber via the merging space.Therefore, the load on the piston is reduced and at the same time theamount of air to be sucked from the outside space can be reduced.

In the present invention, preferably, the valve unit includes:

a discharge valve disposed in the control space and configured to beopened only when the piston is operated in the discharging direction forfeeding air as the fluid from the pressure increasing/decreasing spaceto a pressurizing object as the pressurizing/depressurizing object;

an intake valve disposed in the feeding/discharging space and configuredto be opened only when the piston is operated in the sucking directionfor sucking air as the fluid to the pressure increasing/decreasingchamber; and

an intake path as the fluid path for feeding fluid sucked via the fluidfilter to the intake valve.

With the above-described arrangement, when the piston is operated in thesucking direction, the air of the outside space is fed, while beingfiltered through the fluid filter, from the merging space via the intakepath as the fluid path to the pressure increasing/decreasing chamber andalso the air of the drive chamber is fed from the ventilation path tothe merging space, and a portion of this air fed to the merging space isfed to the intake path. Conversely, when the piston is operated in thedischarging direction, air from the pressure increasing/decreasingchamber is fed via the discharge valve to a pressurizing object; andalso since a negative pressure is developed in the drive chamber at thetime of this operation, the air of the outside space is sucked into thedrive chamber via the ventilation path while being filtered through thefluid filter and a portion of the air of the intake path is also suckedinto the drive chamber.

In the present invention, preferably, the fluid pump includes a pathblock forming the merging space and an opening defined in a bottom wallof the path block for establishing communication between the interiorspace of the path block and the outside space; and an upper face of thebottom wall is formed with an inclined posture such that the upper faceis positioned lower as it extends toward a position closer to theopening.

With the above arrangement, when water drops are formed inside the pathblock, these water drops will flow along the inclination of the upperface of the bottom wall to reach the opening, through which opening thewater drops will be easily drained to the outside of the path block.

In the present invention, preferably, in an annular area surrounding theopening as its center, there are formed a plurality of vertical wallsextending upward from the upper face of the bottom wall, the mergingspace is formed by the region surrounded by the vertical walls, and thefluid path and the ventilation path are communicated with each otheroutside the merging space.

With the above arrangement, the fluid filter can be easily disposedunder a condition of its movement being restricted by the verticalwalls, e.g. by inserting the fluid filter to the space surrounded by thevertical walls.

In the present invention, preferably, a tubular body may be provided toproject downwards at a position on the side of the lower face of thebottom wall of the path block and surrounding the opening.

With the above arrangement, even when water drops adhere to the bottomwall of the path block, the tubular body will prevent occurrence ofphenomenon of these water drops moving toward the opening. Hence, evenwhen the water drops are frozen, this freezing will not interfere withthe flow of fluid at the opening.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a section view of a vacuum pump relating to a firstembodiment,

FIG. 2 is a perspective view showing a path block as seen from its upperface,

FIG. 3 is a perspective view showing the path block as seen from itslower face,

FIG. 4 is a side view in vertical section of the path block,

FIG. 5 is a section view showing the positional relationship between apiston ring and a communication hole when the piston of the firstembodiment is moved in the discharging direction and sucking direction,and

FIG. 6 is a section view of a compressor relating to a secondembodiment.

DESCRIPTION OF EMBODIMENTS

Next, a first embodiment will be explained with reference to theaccompanying drawings.

Basic Construction

As shown in FIG. 1, a reciprocating type vacuum pump, as an example of afluid pump, comprises a piston 2 mounted inside a cylinder 1 to bemovable back and forth therein, a pressure increasing/decreasing chamberA formed on the side of a cylinder head relative to the piston 2, and adrive chamber B formed opposite the pressure increasing/decreasingchamber A relative to the piston 2 and accommodating a crank mechanism Cfor transmitting a drive force to the piston 2.

This vacuum pump is used as a negative pressure source for a brakebooster (not shown) for an automobile. In operation, when the piston 2is operated in a sucking direction (to the right-hand side in FIG. 1), anegative pressure is developed in the pressure increasing/decreasingchamber A. When the piston 2 is operated in a discharging direction (tothe left-hand side in FIG. 1), air as a fluid is discharged from thepressure increasing/decreasing chamber A to the outside. Incidentally,the use of this vacuum pump is not limited for an automobile. This pumpcan be used in various devices that require a negative pressure and canbe used with a gas other than air as the fluid.

[Specific Construction]

In this vacuum pump, as a valve unit V is disposed at one end (on theside of the cylinder head) of the cylinder 1, this valve unit V and thepiston 2 delimit the pressure increasing/decreasing chamber Atherebetween. Further, as a pump housing 3 is disposed at the other endof the cylinder 1, the interior space of this pump housing 3 forms thedrive chamber B.

The pump housing 3 mounts an electric motor 4, and to a crank arm 5rotatable together with an output shaft 4A of this electric motor 4, abase end of a connecting rod 6 is connected. And, the piston 2 isoperably connected to the leading end of this connecting rod 6. In thisway, the crank mechanism C includes the crank arm 5 and the connectingrod 6. With this arrangement, the crank mechanism C converts therotational drive force of the output shaft 4A of the electric motor 4 toa reciprocal operational force and transmits this force to the piston 2,whereby the piston 2 is moved back and forth, i.e. in reciprocation.

The drive chamber B is configured such that a space opened laterally inthe pump housing 3 is closed by a plate-like closure member 7. Thisclosure member 7 defines a ventilation opening 7A. A path block 15having an interior space communicated with this ventilation opening 7Ais mounted on the lower face of the closure member 7 on the outer sidethereof. And, this path block 15 and the closure member 7 are fixedlyconnected to the pump housing 3 with a fastener bolt 8. Further, atubular portion 16 communicated with the interior space of the pathblock 15 is provided in the form of a projection toward the valve unitV.

The valve unit V includes an intake valve 22 mounted at a positionthereof communicated with a sucking space 21A (an example of “a controlspace”) of a valve body 21 and a discharge valve 23 at a portioncommunicated with a discharging space 21B (an example of “afeeding/discharging space”) of this valve body 21. The valve unit Vfurther includes a cover plate 24 for isolating the sucking space 21Aand the discharging space 21B from the outside. To this cover plate 24,there is connected a tube 25 for applying a negative pressure to anexternal brake booster (an example of “a pressurizing/depressurizingobject”). The intake valve 22 is formed of a material such as a resinwhich is flexibly deformable. In operation, when the flow of air is tobe blocked, its rip portion at the outer perimeter is placed in tightcontact with the valve body 21. When the flow of air is to be allowed,the rip portion will float off the valve body 21 to form a space forallowing the air flow. Further, the discharge valve 23 is configured tobe urged by a spring 23S toward its closing direction. Then, when theair flow is to be blocked, with the urging force of the spring 23S, theouter perimeter of the valve 23 is placed into tight contact with thevalve body 21. When the air flow is to be allowed, the outer perimeterwill float off the valve body 21 against the urging force of the spring23S to form a space for allowing the air flow. Incidentally, as theintake valve 22 and the discharge valve 23, a ball or poppet or the likewhich is urged by a spring toward the closing direction or a plate-likemember operable with a hinge may be employed.

The valve body 21 includes a tubular projecting portion 26 communicatedwith the discharging space 21B, with the projecting portion 26projecting toward the pump housing 3. A tubular connecting pipe 9 isprovided for interconnecting this projecting portion 26 and the tubularportion 16 under a mutually communicated state, and this connecting pipe9 has one end thereof fitted on the projecting portion 26 and the otherend thereof fitted on the tubular portion 16.

The valve unit V is connected to the pump housing 3 in such a mannerthat the leading ends of connecting bolts 10 inserted to through holesof the valve body 21 and the cover plate 24 are threaded into femalethread portions of the pump housing 3. This connection is done with aplurality of connecting bolts 10. At the time of this connection, thecylinder 1 will be bound between the valve unit V and the pump housing 3and the connecting pipe 9 is bound between the valve unit V and the pathblock 15, whereby these components are united together.

A ventilation path F is formed to extend from the ventilation opening 7Athrough the interior space of the path block 15 to be communicated withan opening 15H defined in the outer face of the path block 15. A fluidpath E, functioning as a discharge path, is formed to extend from thedischarging space 21B of the valve body 21 trough the connecting pipe 9to be communicated with the interior space of the path block 15. Thisfluid path E is merged in a merging space G formed at an intermediateposition of the ventilation path F, and an air filter 17 (an example of“a fluid filter”) is mounted in this merging space G.

This vacuum pump, as shown in FIG. 1, is designed to be used under aposture that the electric motor 4 is disposed at an upper portion andthe path block 15 is disposed at the lower side. The path block 15, asshown in FIGS. 2-4, is configured such that at an upper position of ablock body having a circular bottom wall 15A and a tubular wall 15Bcontinuous from the outer perimeter of the wall 15A, a laterallyprojecting flange body 15C is formed integral therewith. The flange body15C defines bolt holes 15D in which fastener bolts 8 are to be inserted,and at a position surrounding the block body, there is formed a sealgroove 15E for accommodating a seal 19.

At the center position of the bottom wall 15A, there is defined anopening 15H which establishes communication between the interior spaceof the path block 15 and the outside space. And, the upper face of thisbottom wall 15A is formed with an inclined posture such that the upperface is positioned lower as it extends toward a position closer to theopening 15H. In the upper face of this bottom wall 15A and within anannular area surrounding the opening 15H, there are formed a pluralityof vertical walls 15F rising from the bottom wall 15A and formedintegral with the bottom wall 15A. Reinforcing ribs 15G interconnectingthese plurality of vertical walls 15F and the bottom wall 15A are formedas extending radially about the opening 15H. Through the gaps formedbetween adjacent vertical walls 15F, water can be caused to flow alongthe inclination of the upper face of the bottom wall 15A. The dimensionof the vertical wall 15F in the vertical direction is set shorter thanthe distance from the upper face of the flange body 15C of the pathblock 15 to the bottom wall 15A.

As shown in FIG. 3, on the lower face side of the bottom wall 15A and atthe position surrounding the opening 15H, there is formed a tubular body15L formed integral with the bottom wall 15A, the tubular body 15Lhaving a cylindrical form and projecting downwards. Rib bodies 15Minterconnecting this tubular body 15L and the lower face of the bottomwall 15A are formed to extend radially about the opening 15H.

On the lateral wall of this path block 15, the tubular portion 16mentioned above is formed. And, this tubular portion 16 is communicatedwith the interior space of the block body consisting of the bottom wall15A and the cylindrical wall 15B. Further, an arrangement is providedsuch that when this path block 15 is connected to the closure member 7,the ventilation opening 7A defined in the closure member 7 iscommunicated with the interior space of the block body.

In particular, of the interior space of the path block 15, the spacesurrounded by the vertical walls 15F forms a filter space in which anair filter 17 is to be mounted and a hollow type silencer 18 is formedin the form of a doughnut shape surrounding this filter space. Asilencer space constituting this silencer 18 and the filter spacetogether form the merging space G. Incidentally, the filter space isformed midway in a ventilation path F on the outside air side (the sidecloser to the opening 15H than the filter space) of the merging space G.The silencer space constituting the silencer 18 and the filter space areformed between the outer wall of the closure member 7 and the inner wallof the path block 15. In the filter space, the air filter 17 is mountedas being placed in tight contact with the outer wall of the closuremember 7 and the inner wall of the path block 15. This air filter 17employs wool felt, paper material, urethane foam, etc. having dustremoving property.

That is, the path block 15 has the interior space that constitutes thefluid path E, the ventilation path F and the merging space G, and alsorealizes dust removal and moisture removal by the air filter 17 as wellas noise reduction by the silencer 18. Further, as the bottom wall 15Aof the path block 15 is formed with an inclination, water drops formedinside or moisture removed by the air filter 17 are caused to flowtoward the opening 15H along the inclination of the upper face of thebottom wall 15A to be drained through this opening 15H to the outside.

As the tubular body 15L projects from the lower face of the bottom wall15A, even when water drop adhere to the lower face of the bottom wall15A and freeze thereon, it is possible to avoid inconvenience of thesewater drops being frozen in the vicinity of the opening 15H, so that theventilation condition of the opening 15H can be maintained favorably.Incidentally, the downward projection amount of the tubular body 15L isset smaller than the downward projection amount of the head of thefastener bolt 8, thereby to restrict damage to this tubular body 15L.

[Piston Ring]

As shown in FIG. 5, along the entire perimeter of the outercircumference of the piston 2, an annular groove 2G is formed and apiston ring 30 is fitted with a width narrower than the groove width ofthe annular groove 2G, with the ring 30 being displaceable within thisannular groove 2G along the width direction (the operational directionof the piston 2). Further, in the outer circumference of the piston 2, apiston guide bush 31 is fitted. In the inner perimeter face of thecylinder 1, the piston ring 30 and the piston guide bush 31 are placedin contact with each other and the outer perimeters at the opposed endsof the piston 2 are placed out of contact with the inner perimeter faceof the cylinder 1. The annular groove 2 includes a first lateral wall2Ga on the side of the pressure increasing/decreasing chamber, a secondlateral wall 2Gb on the side of the drive chamber, and a bottom wall 2Gclocated therebetween and forming the bottom of the annular groove 2G.The piston ring 30 has a triple construction formed of an inner ring30A, an intermediate ring 30B and an outer ring 30C superposed with eachother.

The inner ring 30A is formed of stainless steel and defining a slit atthe ring portion. The intermediate ring 30B and the outer ring 30C areformed of polytetrafluoroethyelene resin and form a slit at the ringportion, respectively. Incidentally, the slits of the inner ring 30A,the intermediate ring 30B and the outer ring 30C do not differ fromthose ordinarily formed for facilitating extension of the inner diameterwhen being fitted in the annular groove 2G. Further, relative to theslit of the inner ring 30A, the position of the slit of the intermediateslit 30B is set with 180 degree angular difference, and relative to thisposition of the slit of the intermediate ring 30B, the slit of the outerring 30C is set with 180 degree angular difference. With thesearrangements, there is provided improvement in the sealing performance.

This piston ring 30 is subject to an urging force for increasing theradius of the inner ring 30A. And, with this urging force, the outerperimeter of the outer ring 30C is placed into contact with the innerperimeter face of the cylinder 1 and a gap is formed between the innerperimeter face of the inner ring 30A and the bottom wall 20Gc of theannular groove 2G.

A plurality of communication holes 2T are formed for establishingcommunication between the bottom wall 2Gc of the annular groove 2G andthe interior of the piston 2. The communication holes 2T arecommunicated with the drive chamber B. And, when the piston 2 isoperated in the sucking direction, as illustrated in FIG. 5 (b), thepiston ring 30 is displaced toward the first lateral wall 2Ga toeventually come into contact with this first lateral wall 2Ga, thusblocking flow of air from the pressure increasing/decreasing chamber Atoward the communication holes 2T. Conversely, when the piston 2 isoperated in the discharging direction, as illustrated in FIG. 5 (a),this piston ring 30 is displaced toward the second lateral wall 2Gb toeventually come into contact with this second lateral wall 2Gb, thusforming a gap between this piston ring 30 and the first lateral wall 2G;hence, the flow of air from the pressure increasing/decreasing chamber Atoward the communication holes 2T is allowed.

Operation Mode of First Embodiment

With the above-described configuration, when the piston 2 is operated inthe sucking direction, the piston ring 30 is displaced to the positionin contact (gapless contact) with the first lateral wall 2Ga, thusblocking the flow of air from the pressure increasing/decreasing chamberA toward the drive chamber B. In response to this operation of thepiston 2, the intake valve 22 is opened to suck the air from the tube 25into the pressure increasing/decreasing chamber A to provide a negativepressure, whereby the air of the drive chamber B is fed via theventilation opening 7A into the ventilation path F and discharged viathe opening 15H to the outside of the pump.

Further, when the piston 2 is operated in the discharging direction, thedischarge valve 23 is opened to send the air from the pressureincreasing/decreasing chamber A to the fluid path E. Simultaneously withthis, the piston ring 30 is displaced to the position in contact withthe second lateral wall 2Gb, so that the air of the pressureincreasing/decreasing chamber A is sent via the gap between the pistonring 30 and the first lateral wall 2Ga to the communication holes 2T.With this operation, the drive chamber B reaches a negative pressurecondition. However, since the air is fed via the communication holes 2Tinto the drive chamber B, the degree of the negative pressure is low;hence, the amount of air drawn via the ventilation opening 7A into thedrive chamber B is reduced. In particular, since the ventilation path Ffor feeding air to the communication opening 7A is merged with the fluidpath E (discharge path) in the merging space G, it is possible to feedthe air from the fluid path E (discharge path) to the ventilation pathF. Hence, even when air is drawn into the drive chamber B under thenegative pressure, the air of the fluid path E (discharge path) and theair drawn via the opening 15H will be mixed. As a result, the amount ofambient air to be drawn can be reduced. Incidentally, when air is suckedvia the opening 15H, air filtered through the air filter 17 will besucked. Hence, dust and/or moisture (water content) will be removed bythe air filter 17 and will not enter the drive chamber B.

Moreover, when the piston 2 is operated in the discharging direction,the air of the pressure increasing/decreasing chamber A will flowdirectly into the drive chamber B via the communication holes 2T. Hence,this drive chamber B restricts build-up of negative pressure, thusreducing the drive load variation, whereby the drive torque of theelectric motor 4 is rendered stable. Further, as the electric motor 4 isdriven under a constant load, there occurs no change in the powersupplied to the electric motor 4. As a result, the durability of theelectric motor 4 is improved. When the piston 2 is moved back and forth,there occur intermittent flows of the air of the fluid path E and theventilation path F, and in association with pressure variation, noisewill be generated. But, the silencer 18 reduces this noise.

Incidentally, in this first embodiment, it is possible to employ asimple arrangement of the piston ring 30 being provided in the piston 2,without forming the communication holes 2T in the piston 2.

Next, a second embodiment of the present invention will be describedwith reference to the accompanying drawings.

[Basic Construction]

As shown in FIG. 6, a reciprocating type compressor, as an example of afluid pump, comprises a piston 2 mounted inside a cylinder 1 to bemovable back and forth therein, a pressure increasing/decreasing chamberA formed on the side of the cylinder head relative to the piston 2, anda drive chamber B formed opposite the pressure increasing/decreasingchamber A relative to the piston 2 and accommodating a crank mechanism Cfor transmitting a drive force to the piston 2.

With this compressor in operation, when the piston 2 is operated in asucking direction (to the right-hand side in FIG. 6), air as a fluid issucked into the pressure increasing/decreasing chamber A. When thepiston 2 is operated in an discharging direction (to the left-hand sidein FIG. 1), compressed air as a fluid is discharged from the pressureincreasing/decreasing chamber A to the outside. Incidentally, thiscompressor can be used for a gas other than air as the fluid.

[Specific Construction]

In this compressor, as compared with the first embodiment, thearrangement of the valve unit V differs and the compressor differs alsoin that the piston 2 does not have the communication holes 2T. The restof the arrangement is identical to that of the first embodiment.

Namely, as the valve unit V is disposed at one end (the side of cylinderhead) of the cylinder 1, a pressure increasing/decreasing chamber A isformed between this valve unit V and the piston 2. Further, as a pumphousing 3 is disposed at the other end of the cylinder 1, a drivechamber B is formed by the interior space of this pump housing 3.

The pump housing 3 mounts an electric motor 4, and to a crank arm 5rotatable together with an output shaft 4A of this electric motor 4, abase end of a connecting rod 6 is connected. And, the piston 2 isoperably connected to the leading end of this connecting rod 6. In thisway, the crank mechanism C includes the crank arm 5 and the connectingrod 6.

The drive chamber B is configured such that a space opened laterally inthe pump housing 3 is closed by a plate-like closure member 7. Thisclosure member 7 defines a ventilation opening 7A. A path block 15having an interior space communicated with this ventilation opening 7Ais mounted on the outer side of the closure chamber 7. And, this pathblock 15 and the closure member 7 are fixedly connected to the pumphousing 3 with a fastener bolt 8. Further, a tubular portion 16communicated with the interior space of the path block 15 is provided inthe form of a projection from the path block 15 toward the valve unit V.

The valve unit V includes an intake valve 22 mounted at a positionthereof communicated with a sucking space 21A (an example of “afeeding/discharging space”) of a valve body 21 and a discharge valve 23at a portion communicated with a discharging space 21B (an example of “acontrol space”) of this valve body 21. The valve unit V further includesa cover plate 24 for isolating the sucking space 21A and the dischargingspace 21B from the outside. To this cover plate 24, there is connected atube 25 for feeding compressed air from the pressureincreasing/decreasing chamber A to an external pressurizing object (anexample of “a pressurizing/depressurizing object”). The intake valve 22is formed of a material such as rubber or a resin which is flexiblydeformable. In operation, when the flow of air is to be blocked, its ripportion at the outer perimeter is placed in tight contact with the valvebody 21. When the flow of air is to be allowed, the rip portion willfloat off the valve body 21 to form a space for allowing the air flow.Further, the discharge valve 23 is configured to be urged by a spring23S toward its closing direction. Then, when the air flow is to beblocked, with the urging force of the spring 23S, the outer perimeter ofthe discharge valve 23 is placed into tight or gapless contact with thevalve body 21. When the air flow is to be allowed, the outer perimeterwill float off the valve body 21 against the urging force of the spring23S to form a space for allowing the air flow.

The valve body 21 includes a tubular projecting portion 26 communicatedwith the sucking space 21A, with the projecting portion 26 projectingtoward the pump housing 3. A tubular connecting pipe 9 is provided forinterconnecting this projecting portion 26 and the tubular portion 16under a mutually communicated state, and this connecting pipe 9 has oneend thereof fitted on the projecting portion 26 and the other endthereof fitted on the tubular portion 16.

The valve unit V is connected to the pump housing 3 in such a mannerthat the leading ends of connecting bolts 10 inserted to through holesof the valve body 21 and the cover plate 24 are threaded into femalethread portions of the pump housing 3. This connection is done with aplurality of connecting bolts 10. At the time of this connection, thecylinder 1 will be bound between the valve unit V and the pump housing 3and the connecting pipe 9 is bound between the valve unit V and the pathblock 15, whereby these components are united together.

A ventilation path F is formed to extend from the ventilation opening 7Athrough the interior space of the path block 15 to be communicated withan opening 15H defined in the outer face of the path block 15. A fluidpath E, functioning as an intake path, is formed to extend from thesucking space 21A of the valve body 21 through the connecting pipe 9 tobe communicated with the interior space of the path block 15. This fluidpath E is merged in a merging space G formed at an intermediate positionof the ventilation path F, and an air filter 17 (an example of “a fluidfilter”) is mounted in this merging space G.

In particular, of the interior space of the path block 15, the spacesurrounded by the vertical walls 15F forms a filter space in which theair filter 17 is to be mounted and a hollow type silencer 18 is formedin the form of a doughnut shape surrounding this filter space. Asilencer space constituting this silencer 18 and the filter spacetogether form the merging space G. Incidentally, the filter space isformed midway in a ventilation path F on the outside air side (the sidecloser to the opening 15H than the filter space) of the merging space G.The silencer space constituting the silencer 18 and the filter space areformed between the outer wall of the closure member 7 and the inner wallof the path block 15. In the filter space, the air filter 17 is mountedas being placed in tight contact with the outer wall of the closuremember 7 and the inner wall of the path block 15. This air filter 17employs wool felt, paper material, urethane foam, etc. having dustremoving property.

Incidentally, like the first embodiment, the path block 15 has theinterior space that constitutes the fluid path E, the ventilation path Fand the merging space G, and also realizes dust removal and moistureremoval by the air filter 17 as well as noise reduction by the silencer18. Further, as the bottom wall 15A of the path block 15 is formed withan inclination, water drops formed inside or moisture removed by the airfilter are caused to flow toward the opening 15H along the inclinationof the upper face of the bottom wall 15A to be drained through thisopening 15H to the outside.

Further, along the entire perimeter of the outer circumference of thepiston 2, an annular groove is formed and a piston ring 30 is fittedtherein. Though not shown in details, this piston ring 30 has aconstruction formed by superposing a plurality of rings from the innerside to the outer side. And, the outermost ring employspolytetrafluoroethyelene resin. Along the outer perimeter of the piston2, a piston guide bush 31 is fitted therein, and in the inner perimeterface of the cylinder 1, the piston ring 30 and the piston guide bush 31are placed in contact with each other and the outer perimeters at theopposed ends of the piston 2 are out of contact with the inner perimeterface of the cylinder 1.

Operation Mode of Second Embodiment

With the above-described configuration, when the piston 2 is operated inthe sucking direction, the intake valve 22 is opened, whereby air of theexternal space is sucked through the opening 15H and filtered throughthe air filter 17 and then fed via the fluid path E (intake path) intothe pressure increasing/decreasing chamber A. When this suctionoperation is effected, there occurs increase in the pressure of thedrive chamber B. So that, the air of the drive chamber B is sent out tothe ventilation path F and a portion of this air is merged in themerging space G (the filter space and the silencer space) and fed to thefluid path E. That is, when the piston 2 is operated in the suckingdirection, ambient air and the air fed from the drive chamber B aremerged in the merging space G and fed to the pressureincreasing/decreasing chamber A.

Further, when the piston 2 is operated in the discharging direction(compressing direction), the discharge valve 23 is opened whereby theair from the pressure increasing/decreasing chamber A is fed to the tube25. Simultaneously therewith, a negative pressure is developed in thedrive chamber B. Thus, ambient air is fed via the opening 15H to theventilation path F and sucked into the drive chamber B and also aportion of the air of the fluid path E is sucked as being merged in themerging space G. That is, when the piston 2 is operated in thedischarging direction, the fluid path E is placed out of communicationwith the pressure increasing/decreasing chamber A, but when the drivechamber B reaches a negative pressure, air can be sent out like achamber. Hence, the amount of air to be sucked from the outside spacecan be reduced. Further, since the ambient air to be sucked into thedrive chamber B is always filtered through the air filter 17, dustand/or moisture (water content) are removed by the air filter 17 andwill not enter the drive chamber B.

Further, at the time of operations of the piston 2, when the piston 2 isoperated in the sucking direction, the air of the drive chamber B issent out. When the piston 2 is operated in the discharging direction,the air is sucked into the drive chamber B. Therefore, the variation inthe pressure of the drive chamber B can be restricted, so that the drivetorque of the electric motor 4 is rendered stable. Further, as theelectric motor 4 is driven under a constant load, there occurs no changein the power supplied to the electric motor 4. As a result, thedurability of the electric motor 4 is improved. When the piston 2 ismoved back and forth, there occur intermittent flows of the air of thefluid path E and the ventilation path F, and in association withpressure variation, noise will be generated. But, the silencer 18reduces this noise.

INDUSTRIAL APPLICABILITY

The present invention may be used for fluid pumps in general that areconfigured such that a piston is operated inside a cylinder.

1. A fluid pump comprising: a cylinder; a piston mounted inside thecylinder to be moved back and forth, the piston partitioning the insideof the cylinder between a pressure increasing/decreasing chamber on theside of the cylinder head and a drive chamber opposite the pressureincreasing/decreasing chamber; a valve unit having a control space forcausing fluid of the pressure increasing/decreasing chamber to act on apressurizing/depressurizing object and a feeding/discharging space forfeeding/discharging fluid between the pressure increasing/decreasingchamber and the outside space, the valve unit being provided in thecylinder head so as to control flow of the fluid to the pressureincreasing/decreasing chamber at the time of a reciprocal movement ofthe piston: a path block mounted to the cylinder; a ventilation pathcommunicating the drive chamber and the outside space with each othervia the path block; a fluid path connected to the feeding/dischargingspace and the path block so as to be merged with the ventilation path ina merging space inside the path block; a fluid filter mounted in themerging space; and an opening defined in a bottom wall of the path blockfor establishing communication between the interior space of the pathblock and the outside space; and wherein an upper face of the bottomwall is formed with an inclined posture such that the upper face ispositioned lower as it extends toward a position closer to the opening.2. The fluid pump according to claim 1, wherein the valve unit includes:an intake valve disposed in the control space and configured to beopened only when the piston is operated in the sucking direction forsucking air as the fluid from a depressurizing object as thepressurizing/depressurizing object to the pressure increasing/decreasingchamber; a discharge valve disposed in the feeding/discharging space andconfigured to be opened only when the piston is operated in thedischarging direction for feeding air as the fluid to the pressureincreasing/decreasing space; and a discharging path as the fluid pathfor feeding air from the discharge valve to the merging space.
 3. Thefluid pump according to claim 1, wherein the valve unit includes: adischarge valve disposed in the control space and configured to beopened only when the piston is operated in the discharging direction forfeeding air as the fluid from the pressure increasing/decreasing spaceto a pressurizing object as the pressurizing/depressurizing object; anintake valve disposed in the feeding/discharging space and configured tobe opened only when the piston is operated in the sucking direction forsucking air as the fluid to the pressure increasing/decreasing chamber;and an intake path as the fluid path for feeding fluid sucked via thefluid filter to the intake valve.
 4. (canceled)
 5. The fluid pumpaccording to claim 1, wherein in an annular area surrounding the openingas its center, there are formed a plurality of vertical walls extendingupward from the upper face of the bottom wall, the merging space isformed by the region surrounded by the vertical walls, and the fluidpath and the ventilation path are communicated with each other outsidethe merging space.
 6. The fluid pump according to claim 1, wherein atubular body is provided to project downwards at a position on the sideof the lower face of the bottom wall of the path block and surroundingthe opening.